When working with a map-supported navigation system, conventional systems are used to determine position using a composite-navigation process in which the data supplied by the sensors of a motor vehicle are compared to those of a digital road map. The vehicle position determined by the composite-navigation process is corrected, the vehicle being placed on a street that runs nearby. However, if many streets run at a similar angle relative to the travel direction of the vehicle, it is possible that the vehicle may be positioned on the wrong street. As it continues its trip, the vehicle remains on this "incorrect street", since no other test is performed to check the accuracy of this positional correction.
European Patent Application No. 0 314 806 describes that a range of error is determined for the estimated vehicle position, whose magnitude is predetermined by the tolerances of the sensors for the length of travel and the driving direction. By means of a computer, those vehicle positions, which are transmitted for a given driving situation, are calculated for all streets within the range of error. By estimating the distances and other parameters, the vehicle position whose street characteristic curve comes the closest is determined to be the actual position. In this conventional method, the problem arises that when working with a narrow network of streets having several parallel routes situated closely together, the street can not always be found on which the vehicle is actually driving.